Cardiovascular disease is a major health risk throughout the industrialized world. Atherosclerosis, the most prevalent of cardiovascular diseases, is the principal cause of heart attack, stroke, and gangrene of the extremities, and thereby the principal cause of death in the United States. Atherosclerosis is a complex disease involving many cell types and molecular factors (for a detailed review, see Ross, 1993, Nature 362: 801-809).
Ischemia is a condition characterized by a lack of oxygen supply in tissues of organs due to inadequate perfusion. Such inadequate perfusion can have number of natural causes, including atherosclerotic or restenotic lesions, anemia, or stroke, to name a few. Many medical interventions, such as the interruption of the flow of blood during bypass surgery, for example, also lead to ischemia. In addition to sometimes being caused by diseased cardiovascular tissue, ischemia may sometimes affect cardiovascular tissue, such as in ischemic heart disease. Ischemia may occur in any organ, however, that is suffering a lack of oxygen supply.
The most common cause of ischemia in the heart is myocardial infarction (MI), commonly known as a heart attack, is one of the most well-known types of cardiovascular disease. 1998 estimates show 7.3 million people in the United States suffer from MI, with over one million experiencing an MI in a given year (American Heart Association, 2000). Of these individuals, 25% of men, and 38% of females will die within a year of their first recognized MI (American Heart Association, 2000). MI is caused by a sudden and sustained lack of blood flow to an area of the heart, commonly caused by narrowing of a coronary artery. Without adequate blood supply, the tissue becomes ischemic, leading to the death of myocytes and vascular structures. This area of necrotic tissue is referred to as the infarct site, and will eventually become scar tissue. Survival is dependent on the size of this infarct site, with the probability of recovery decreasing with increasing infarct size. For example, in humans, an infarct of 46% or more of the left ventricle triggers irreversible cardiogenic shock and death (99).
Current treatments for MI focus on reperfusion therapy, which attempts to start the flow of blood to the affected area to prevent the further loss of tissue. The main choices for reperfusion therapy include the use of anti-thrombolytic agents, or performing balloon angioplasty, or a coronary artery bypass graft. Anti-thrombolytic agents solubilize blood clots that may be blocking the artery, while balloon angioplasty threads a catheter into the artery to the site of the occlusion, where the tip of the catheter is inflated, pushing open the artery. Still more invasive procedures include the bypass, where surgeons remove a section of a vein from the patient, and use it to create a new artery in the heart, which bypasses the blockage, and continues the supply of blood to the affected area. In 1998, there were an estimated 553,000 coronary artery bypass graft surgeries and 539,000 percutaneous transluminal coronary angioplastys. These procedures average $27,091 and $8,982 per patient, respectively (American Heart Association, 2000).
These treatments may succeed in reestablishing the blood supply, however tissue damage that occurred before the reperfusion treatment began has been thought to be irreversible. For this reason, eligible MI patients are started on reperfusion therapy as soon as possible to limit the area of the infarct.
As such, most studies on MI have also focused on reducing infarct size. There have been a few attempts to regenerate the necrotic tissue by transplanting cardiomyocytes or skeletal myoblasts (Leor et al., 1996; Murray, et al., 1996; Taylor, et al., 1998; Tomita et al., 1999; Menasche et al., 2000). While the cells may survive after transplantation, they fail to reconstitute healthy myocardium and coronary vessels that are both functionally and structurally sound.
All of the cells in the normal adult originate as precursor cells which reside in various sections of the body. These cells, in turn, derive from very immature cells, called progenitors, which are assayed by their development into contiguous colonies of cells in 1-3 week cultures in semisolid media such as methylcellulose or agar. Progenitor cells themselves derive from a class of progenitor cells called stem cells. Stem cells have the capacity, upon division, for both self-renewal and differentiation into progenitors. Thus, dividing stem cells generate both additional primitive stem cells and somewhat more differentiated progenitor cells. In addition to the well-known role of stem cells in the development of blood cells, stem cells also give rise to cells found in other tissues, including but not limited to the liver, brain, and heart.
Stem cells have the ability to divide indefinitely, and to specialize into specific types of cells. Totipotent stem cells, which exist after an egg is fertilized and begins dividing, have total potential, and are able to become any type of cell. Once the cells have reached the blastula stage, the potential of the cells has lessened, with the cells still able to develop into any cell within the body, however they are unable to develop into the support tissues needed for development of an embryo. The cells are considered pluripotent, as they may still develop into many types of cells. During development, these cells become more specialized, committing to give rise to cells with a specific function. These cells, considered multipotent, are found in human adults and referred to as adult stem cells. It is well known that stem cells are located in the bone marrow, and that there is a small amount of peripheral blood stem cells that circulate throughout the blood stream (National Institutes of Health, 2000).
Due to the regenerative properties of stem cells, they have been considered an untapped resource for potential engineering of tissues and organs. It would be an advance to provide uses of stem cells with respect to addressing cardiac conditions.
Mention is made of:
U.S. Pat. No. 6,117,675 which relates to the differentiation of retinal stem cells into retinal cells in vivo or in vitro, which can be used as a therapy to restore vision.
U.S. Pat. No. 6,001,934 involving the development of functional islets from islets of Langerhans stem cells.
U.S. Pat. Nos. 5,906,934 and 6,174,333 pertaining to the use of mesenchymal stem cells for cartilage repair, and the use of mesenchymal stem cells for regeneration of ligaments; for instance, wherein the stem cells are embedded in a gel matrix, which is contracted and then implanted to replace the desired soft tissue.
U.S. Pat. Nos. 6,099,832, and 6,110,459 involving grafts with cell transplantation.
PCT Application Nos. PCT/US00/08353 (WO 00/57922) and PCT/US99/17326 (WO 00/06701) involving intramyocardial injection of autologous bone marrow and mesenchymal stem cells which fails to teach or suggest administering, implanting, depositing or the use of hematopoietic or cardiac stem cells as in the present invention, especially as the hematopoietic and cardiac stem cells as in the present invention are advantageously isolated and/or purified adult hematopoietic or cardiac stem cells.
Only recent literature has started to investigate the potentials for stem cells to aid in the repair of tissues other than that of known specialization. This plasticity of stem cells, the ability to cross the border of germ layers, is a concept only in its infancy (Kempermann et al, 2000, Temple, 2001). Kocher et al (2001) discusses the use of adult bone marrow to induce neovascularization after infarction as an alternative therapy for left ventricle remodeling (reviewed in Rosenthal and Tsao, 2001). Other studies have focused on coaxing specific types of stem cells to differentiate into myocardial cells, e.g. liver stem cells as shown in Malour et al. (2001). Still other work focuses on the possibilities of bone-marrow derived stem cells (Krause, et al., 2001).
One of the oldest uses of stem cells in medicine is for the treatment of cancer. In these treatments, bone marrow is transplanted into a patient whose own marrow has been destroyed by radiation, allowing the stem cells in the transplanted bone marrow to produce new, healthy, white blood cells.
In these treatments, the stem cells are transplanted into their normal environment, where they continue to function as normal. Until recently, it was thought that any particular stem cell line was only capable of producing three or four types of cells, and as such, they were only utilized in treatments where the stem cell was required to become one of the types of cells for which their ability was already proven. Researchers are beginning to explore other options for treatments of myriad disorders, where the role of the stem cell is not well defined.
Organ transplantation has been widely used to replace diseased, nonfunctional tissue. More recently, cellular transplantation to augment deficiencies in host tissue function has emerged as a potential therapeutic paradigm. One example of this approach is the well publicized use of fetal tissue in individuals with Parkinsonism (reviewed in Tompson, 1992), where dopamine secretion from transplanted cells alleviates the deficiency in patients. In other studies, transplanted myoblasts from unaffected siblings fused with endogenous myotubes in Duchenne's patients; importantly the grafted myotubes expressed wild-type dystrophin (Gussoni et al., 1992).
Despite their relevance in other areas, these earlier studies do not describe any cellular transplantation technology that can be successfully applied to the heart, where the ability to replace damaged myocardium would have obvious clinical relevance. Additionally, the use of intra-cardiac grafts to target the long-term expression of angiogenic factors and ionotropic peptides would be of therapeutic value for individuals with myocardial ischemia or congestive heart failure, respectively.
In light of this background there is a need for the improvement of myocardial regeneration technology in the heart. Desirably, such technology would not only result in tissue regeneration in the heart but also enable the delivery of useful compositions directly to the heart. The present invention addresses these needs.